1. Field of the Invention
This invention relates generally to an axial air-gap motor and, more particularly, to a spindle motor that includes a magnet for holding a recording disc.
2. Description of the Background
Generally, the spindle motor used for driving a magnetic record disc, such as the well-known floppy disc, is of the axial air-gap type. This motor is typically brushless and, in order to chuck the disc, employs a magnet on the rotor to attract the magnetic center core of the floppy disc and hold it firmly. The properly chucked floppy disc is then rotated by the spindle motor. More specifically, the magnetic center core of the floppy disc is attracted by the magnet that is formed on an upper portion of the rotor of the spindle motor. Such a brushless spindle motor typically employs a rotor that includes a housing that is rotatably supported on an axle by means of upper and lower bearings. The rotor then includes a ring-shaped disc-attracting magnet that is affixed to the housing and that projects upwardly toward the floppy disc. The rotor further includes a circular disc-shaped rotor yoke that is formed of magnetic metal and is fitted onto a portion of the housing that is concentric with the axle. A ring-shaped rotor magnet is adhesively affixed to the lower surface of the rotor yoke.
In those situations where it is necessary to increase the forces of magnetic attraction exerted on the center core of the magnetic disc that hold it against the housing of the rotor, the housing can be formed of magnetic material. On the other hand, there are situations in which this magnetic metal housing provides a disadvantage in that it prevents easy detection of the rotation of the magnetic record disc that would otherwise be possible by detecting leakage magnetic flux from the magnet used to hold the disc against the housing. When such disc rotation detection is required, the leakage magnetic flux is more easily detected if the housing is made of non-magnetic material, such as aluminum, for example.
The stator that supports the axle of the rotor housing includes a base table having a U-shaped cross section that is affixed to the axle by means of a boss. A coil substrate is affixed to the upper surface of the base table by suitable fasteners, such as screws, and faces the rotor magnet with a predetermined clearance. A plurality of stator coils are disposed on the facing surface of the coil substrate and are equally spaced around the axle with a predetermined clearance from the rotor magnet.
Upon appropriately mounting the magnetic disc on the rotor, the magnetic forces of the disc-attracting magnet affixed to the rotor housing cause the center core of the magnetic record disc to be attracted thereto and firmly held to the upper mounting surface of the housing. Thus, upon application of power to the motor, in this case to the coils of the stator, the rotor will turn and thereby rotate the magnetic sheet of the floppy disc along with the rotor.
During manufacture and assembly of the housing and rotor yoke of this known brushless, axial air-gap motor, there are a large number of methods and machining processes involved, as well as the requirement for a large number of parts. Thus, the total man hours required to assemble the rotor of such a motor is quite high relative to the overall motor assembly. Accordingly, manufacturing costs for this kind of spindle motor, as presently known, are much higher than desired. Furthermore, because both the housing and the rotor yoke are formed of magnetic metallic materials, the total weight of the rotor is increased beyond what is desirable.